public static string Generate(int minLength,
int maxLength)
{
if (minLength <= 0 || maxLength <= 0 || minLength > maxLength)
{
return(null);
}
char[][] charGroups = new char[][]
{
PASSWORD_CHARS_LCASE.ToCharArray(),
PASSWORD_CHARS_UCASE.ToCharArray(),
PASSWORD_CHARS_NUMERIC.ToCharArray(),
PASSWORD_CHARS_SPECIAL.ToCharArray()
};
int[] charsLeftInGroup = new int[charGroups.Length];
for (int i = 0; i < charsLeftInGroup.Length; i++)
{
charsLeftInGroup[i] = charGroups[i].Length;
}
int[] leftGroupsOrder = new int[charGroups.Length];
for (int i = 0; i < leftGroupsOrder.Length; i++)
{
leftGroupsOrder[i] = i;
}
byte[] randomBytes = new byte[4];
RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
rng.GetBytes(randomBytes);
int seed = BitConverter.ToInt32(randomBytes, 0);
Random random = new Random(seed);
char[] password = null;
if (minLength < maxLength)
{
password = new char[random.Next(minLength, maxLength + 1)];
}
else
{
password = new char[minLength];
}
int nextCharIdx;
int nextGroupIdx;
int nextLeftGroupsOrderIdx;
int lastCharIdx;
int lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
for (int i = 0; i < password.Length; i++)
{
if (lastLeftGroupsOrderIdx == 0)
{
nextLeftGroupsOrderIdx = 0;
}
else
{
nextLeftGroupsOrderIdx = random.Next(0,
lastLeftGroupsOrderIdx);
}
nextGroupIdx = leftGroupsOrder[nextLeftGroupsOrderIdx];
lastCharIdx = charsLeftInGroup[nextGroupIdx] - 1;
if (lastCharIdx == 0)
{
nextCharIdx = 0;
}
else
{
nextCharIdx = random.Next(0, lastCharIdx + 1);
}
password[i] = charGroups[nextGroupIdx][nextCharIdx];
if (lastCharIdx == 0)
{
charsLeftInGroup[nextGroupIdx] =
charGroups[nextGroupIdx].Length;
}
else
{
if (lastCharIdx != nextCharIdx)
{
char temp = charGroups[nextGroupIdx][lastCharIdx];
charGroups[nextGroupIdx][lastCharIdx] =
charGroups[nextGroupIdx][nextCharIdx];
charGroups[nextGroupIdx][nextCharIdx] = temp;
}
charsLeftInGroup[nextGroupIdx]--;
}
if (lastLeftGroupsOrderIdx == 0)
{
lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
}
else
{
if (lastLeftGroupsOrderIdx != nextLeftGroupsOrderIdx)
{
int temp = leftGroupsOrder[lastLeftGroupsOrderIdx];
leftGroupsOrder[lastLeftGroupsOrderIdx] =
leftGroupsOrder[nextLeftGroupsOrderIdx];
leftGroupsOrder[nextLeftGroupsOrderIdx] = temp;
}
lastLeftGroupsOrderIdx--;
}
}
return(new string(password));
}
public static string GetRandomString(int minLength, int maxLength)
{
const string PASSWORD_CHARS_LCASE = "abcdefgijkmnopqrstwxyz";
const string PASSWORD_CHARS_UCASE = "ABCDEFGHJKLMNPQRSTWXYZ";
const string PASSWORD_CHARS_NUMERIC = "23456789";
const string PASSWORD_CHARS_SPECIAL = "!?$%^)";
if (minLength <= 0 || maxLength <= 0 || minLength > maxLength)
{
return(null);
}
// Create a local array containing supported password characters
// grouped by types. You can remove character groups from this
// array, but doing so will weaken the password strength.
char[][] charGroups = new char[][]
{
PASSWORD_CHARS_LCASE.ToCharArray(),
PASSWORD_CHARS_UCASE.ToCharArray(),
PASSWORD_CHARS_NUMERIC.ToCharArray(),
PASSWORD_CHARS_SPECIAL.ToCharArray()
};
// Use this array to track the number of unused characters in each
// character group.
int[] charsLeftInGroup = new int[charGroups.Length];
// Initially, all characters in each group are not used.
for (int i = 0; i < charsLeftInGroup.Length; i++)
{
charsLeftInGroup[i] = charGroups[i].Length;
}
// Use this array to track (iterate through) unused character groups.
int[] leftGroupsOrder = new int[charGroups.Length];
// Initially, all character groups are not used.
for (int i = 0; i < leftGroupsOrder.Length; i++)
{
leftGroupsOrder[i] = i;
}
// Because we cannot use the default randomizer, which is based on the
// current time (it will produce the same "random" number within a
// second), we will use a random number generator to seed the
// randomizer.
// Use a 4-byte array to fill it with random bytes and convert it then
// to an integer value.
byte[] randomBytes = new byte[4];
// Generate 4 random bytes.
RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
rng.GetBytes(randomBytes);
// Convert 4 bytes into a 32-bit integer value.
int seed = BitConverter.ToInt32(randomBytes, 0);
// Now, this is real randomization.
Random random = new Random(seed);
// This array will hold password characters.
char[] password = null;
// Allocate appropriate memory for the password.
if (minLength < maxLength)
{
password = new char[random.Next(minLength, maxLength + 1)];
}
else
{
password = new char[minLength];
}
// Index of the next character to be added to password.
int nextCharIdx;
// Index of the next character group to be processed.
int nextGroupIdx;
// Index which will be used to track not processed character groups.
int nextLeftGroupsOrderIdx;
// Index of the last non-processed character in a group.
int lastCharIdx;
// Index of the last non-processed group.
int lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
// Generate password characters one at a time.
for (int i = 0; i < password.Length; i++)
{
// If only one character group remained unprocessed, process it;
// otherwise, pick a random character group from the unprocessed
// group list. To allow a special character to appear in the
// first position, increment the second parameter of the Next
// function call by one, i.e. lastLeftGroupsOrderIdx + 1.
if (lastLeftGroupsOrderIdx == 0)
{
nextLeftGroupsOrderIdx = 0;
}
else
{
nextLeftGroupsOrderIdx = random.Next(0,
lastLeftGroupsOrderIdx);
}
// Get the actual index of the character group, from which we will
// pick the next character.
nextGroupIdx = leftGroupsOrder[nextLeftGroupsOrderIdx];
// Get the index of the last unprocessed characters in this group.
lastCharIdx = charsLeftInGroup[nextGroupIdx] - 1;
// If only one unprocessed character is left, pick it; otherwise,
// get a random character from the unused character list.
if (lastCharIdx == 0)
{
nextCharIdx = 0;
}
else
{
nextCharIdx = random.Next(0, lastCharIdx + 1);
}
// Add this character to the password.
password[i] = charGroups[nextGroupIdx][nextCharIdx];
// If we processed the last character in this group, start over.
if (lastCharIdx == 0)
{
charsLeftInGroup[nextGroupIdx] =
charGroups[nextGroupIdx].Length;
}
// There are more unprocessed characters left.
else
{
// Swap processed character with the last unprocessed character
// so that we don't pick it until we process all characters in
// this group.
if (lastCharIdx != nextCharIdx)
{
char temp = charGroups[nextGroupIdx][lastCharIdx];
charGroups[nextGroupIdx][lastCharIdx] =
charGroups[nextGroupIdx][nextCharIdx];
charGroups[nextGroupIdx][nextCharIdx] = temp;
}
// Decrement the number of unprocessed characters in
// this group.
charsLeftInGroup[nextGroupIdx]--;
}
// If we processed the last group, start all over.
if (lastLeftGroupsOrderIdx == 0)
{
lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
}
// There are more unprocessed groups left.
else
{
// Swap processed group with the last unprocessed group
// so that we don't pick it until we process all groups.
if (lastLeftGroupsOrderIdx != nextLeftGroupsOrderIdx)
{
int temp = leftGroupsOrder[lastLeftGroupsOrderIdx];
leftGroupsOrder[lastLeftGroupsOrderIdx] =
leftGroupsOrder[nextLeftGroupsOrderIdx];
leftGroupsOrder[nextLeftGroupsOrderIdx] = temp;
}
// Decrement the number of unprocessed groups.
lastLeftGroupsOrderIdx--;
}
}
// Convert password characters into a string and return the result.
return(new string(password));
}
